We're going after Mexes because he's currently available. He's not that great, just has his moments.
If he's motivated enough to give 100% for Juve, I see him as a decent partner for Chiellini.
But they are not Cannavaro. They are good defenders but they just looked WC in defence because Inter had 2/3 deep cdm's everytime I watched them play last season. I don't rate neither of them that high and don't see them play at this level very long.